MIMO technologies have gradually been applied in practical use to over-the-horizon communication to improve the communication capacity. On the other hand, it has been believed that such MIMO technologies are not suitable for line-of-sight communication. However, Non-Patent Document 1 given below describes that, even in line-of-sight communication, a plurality of orthogonal virtual paths can be generated by devising arrangement of transmission and reception antennas, and the communication capacity can be improved. According to this method, phase rotation of a carrier signal caused by difference in propagation delay is utilized effectively to cancel spurious waves so that independent data paths are formed. When the difference in propagation delay is increased according to spacing between antennas to a significant value for a symbol cycle, inter-symbol interference or interference between unique paths will occur. While the inter-symbol interference can be equalized by a conventional equalizer, the inter-path interference will result in deterioration of communication quality unless appropriate countermeasures are taken.    Non-Patent Document 1: P. F. Driessen, G. J. Foschini; “On the Capacity Formula for Multiple Input-Multiple Output Wireless Channels: A Geometric Interpretation”; IEEE TRANSACTIONS ON COMMUNICATIONS, VOL. 47, No. 2, P. 173, February 1999